AppearanceThe substance is clear and not more intensely colored than a solution prepared immediately before use by mixing 2.4 mL of ferric chloride CS and 0.6 mL of cobaltous chloride CS with dilute hydrochloric acid (10 g per L) to make 10 mL, and diluting 5 mL of this solution with dilute hydrochloric acid (10 g per L) to make 100 mL. Make the comparison by viewing the substance and the solution downward in matched color-comparison tubes against a white surface (see Color and Achromicity 631).

AcidityMix 20.0 g of Dibutyl Phthalate with 50 mL of alcohol that previously has been neutralized to a phenolphthalein endpoint, add 0.2 mL of phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS: not more than 0.50 mL is required to change the color of the indicator.

Chromatographic system (see Chromatography 621)The gas chromatograph is equipped with a flame-ionization detector and contains a 4-mm × 1.5-m column packed with 3% liquid phase G3 on support S1A. The carrier gas is nitrogen, flowing at a rate of about 30 mL per minute. The column temperature is maintained at 190, and the injection port temperature and the detector temperature are maintained at 225. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the elution order is the internal standard peak followed by the dibutyl phthalate peak; and the resolution, R, between these peaks is not less than 12. Chromatograph Test solution 1, and verify that there is no peak with the same retention time as the internal standard. If a peak observed in the chromatogram for Test solution 1 has the same retention time as that for the internal standard, make any necessary correction for factors of dilution, and then determine the area due to the interfering component that must be subtracted from the area of the internal standard peak appearing in the chromatogram recorded for Test solution 2, as directed for Procedure.

ProcedureInject 1-µL portions of Test solution 2 and the Standard solution successively into the gas chromatograph, record the chromatograms for three times the retention time of dibutyl phthalate, and measure the responses of the peaks. From the chromatogram of the Standard solution, calculate the peak area ratio of dibutyl phthalate to the internal standard, A. From the chromatogram of Test solution 2, calculate the peak area ratio of the sum of all peaks, excluding the main peak, the solvent peak, and the internal standard peak, to the internal standard peak: this ratio is not greater than A (1.0%).